The invention described herein relates to waste water treatment systems and more particularly to a system for treating waste waters by contact-stabilization techniques.
Conventional commercial sewage disposal plants contain multiple tanks, associated air systems and sludge disposal means for treating domestic and industrial waste materials. Since waste water treatment systems of this type are expensive to install and maintain and because considerable time is required to properly process the waste waters, consideration has been given in the past to utilizing a contact stabilization system to remove BOD from sewage in a fraction of the time required by the conventional commercial systems. Published information on contact-stabilization systems disclose the use of a baffled aeration tank which serves the function of two tanks and a final clarifier tank, for removing sewage BOD by physical adsorption in 20-30 minutes. The aeration tank serves both contact and stabilization functions by initially aerating the raw influent in the contact aeration portion of the tank and after passing through the clarifier, the other part of the tank which is in open communication with the contact portion, stabilizes the remaining BOD.
The disadvantages inherent in the above described contact-stabilization system is that when tank like structures are used, air discharged into the tank from a diffuser, rises uniformly to the liquid surface in the form of relatively large size bubbles and the desired degree of contact is not made with the suspended solids. As a result, optimum contact of the solids per unit volume of air is not achieved and the air or oxygen system is therefore relatively inefficient. Because of this, the tank must therefore be sized to a large volume. Usually the solids must be removed physically from the system by a bottom rake or similar structure.
Moreover, since the same tank is used for both contact and stabilization purposes, intermixing of untreated and treated liquids occur and the process is therefore not as efficient as when separate tanks are used to secure performance of the separate functions.